Grinding machine and method



Oct. 18, 1960 G. R. WHITE GRINDING MACHINE} AND METHOD 3 Sheets-Sheet 1 Filed July 22, 1957 NVENTOR Geoffrey WMZB /A WWM ATTORNEYS Oct. 18, 1960 e. R. WHITE 2,956,377

GRINDING MACHINE AND METHOD Filed July 22, 1957 3 Sheets-Sheet 2 Ha. P.

FIG. 4.

[NVENTOR Geoffrey 6. W/u'fe- Y Y ATTORNEY.

Oct. 18, 1960 w rr 2,956,377

GRINDING MACHINE AND METHOD Filed July 22, 1957 3 Sheets-Sheet 5 INVENTOR Geo/fray 3 M {8 ATTORNEYS Umomd a es Patent 2,956,377 GRINDING MACHINE AND METHOD Geoffrey Reynault White, Torquay, South Devon, England, assignor to Centrax Power Units Limited, Feltham, England, a British company Filed July 22, 1951, Ser. No. 673,519

Claims priority, application Great Britain Aug. 9, 1956 2 Claims. (Cl. 51-100) This invention relates to machine tools for grinding three dimensional shapes and has particular, although not exclusive, reference to machines and tools for grinding the working portion of turbine and compressor blades.

The existing methods of grinding three dimensional shapes such as turbine or compressor blades involves grinding with a comparatively narrow wheel of curved peripheral section which generates the surface by the wheel and/or the work being moved so that the whole area is ground. Any given tangent angle of the work relative to the peripheral cross section of the wheel is always generated by the same line on the wheel and thus the wheel wear is highest at the mean of the two extremes of tangentiangle and negligible at the extremes. This means that if the correct wheel shape is to be maintained it must be dressed frequently and that, as only a very small area of the wheel is'being used, excessive heating of the wheel and consequently of the work will occur unless comparatively slow grinding speeds are used.

'The objects of the present invention include the provision of a machine in which, by comparison with known machines, the rate of wear of the grinding tool is reduced, the grinding speed may be increased without increasing the heating effect on the tool or the work and the surface finish on the work is improved.

According to the present invention, the surface of a grinding tool such as a wheel or abrasive belt work pulley has an axial width equal or approximately equal to the length of the component or work to be ground and a convex peripheral section. In using a tool embodying the invention, the component or work to be ground is arranged with its longitudinal axis parallel with that of the tool or pulley and is mounted so that it can be rocked in a controlled manner about an axis at 90 to the axis of rotation of the tool or pulley. Preferably also, the component or work is arranged to be fed transversely under the tool or pulley, thus enabling the whole of the surface to be ground.

Alternative forms of machines and tools embodying the invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a side elevation of one such machine,

Figure 2 is a side elevation of one form of grinding wheel and shows the position of the work in relation thereto,

Figure 3 is a front elevation of the wheel shown in Figure 2 and showing the extreme positions of cross feed of the work; and

Figure 4 is a fragmentary side elevation of another form of grinding wheel.

Referring to Figure l of the drawings, the machine 1 is provided with a grinding wheel 2 driven by means not shown and a stylus 3 having a face of similar shape to that of the grinding wheel 2, the latter being mounted to engage a workpiece 4 which, in the example shown, is a turbine blade. A master cam 5 and the workpiece 4 are rigidly mounted on a cradle 6 which is pivotally mounted in bearings 7 so that the cradle may be rocked 2,956,377 Patented Oct. 18, 1960 2 about an axis passing through the bearings, by mechanism 8 which determines the degree of rocking movement.

The cradle 6 may be provided with any known convenient means for clamping the root of the turbine blade workpiece so as to hold it rigidly in position. Thus, there may be used for this purpose and as shown in Fig. l a clamp 6a having two separable members formed with depressed surfaces shaped to correspond with the root of the blade and rigidly clamped together by a bolt the shank of which passes freely through one member and into a screw-threaded engagement with the other.

The mechanism 8 includes an electric motor the shaft of which, via a cam or appropriately shaped pin-and-slot movement, oscillates the arm 8a attached to the cradle pivot 7a, through a predetermined arc.

A fork member 9 which carries the cradle bearings is mounted for movement in slides 10 and a spring 11 urges the fork to the left, as seen in Figure 1, to maintain the stylus 3 and the grinding wheel 2 in pressure contact with the master cam 5 and the workpiece 4 respectively.

A housing 12 for the spring 11 forms an assembly with the fork member 9 and the base portion 13 of this assembly is mounted on slides 14 enabling the assembly to be traversed by a screw drive 15 and operating mechanism 16 which thus serves to cross-feed the workpiece relative to the grinding Wheel 2. A grinding wheel dressing device 18 is mounted on the machine.

In operation of the machine it will be seen that the grinding wheel is only rotated and is not otherwise moved with respect to the work but the latter is rocked by the cradle 6 about an axis as indicated for example at 0 in Figure 2. This figure also shows the convex surface of the grinding wheel 2 and that the axial width of the wheel 2 is approximately equal to the length of the blade 4 being ground. Figure 3 illustrates the extremes of cross feed of the workpiece 4 from the full line to the dotted line position. In operation of the machine the rocking motion and the cross-feed are superimposed on each other, i.e., are efiected simultaneously.

Referring now to Figure 4 of the drawings, the modified shape of the grind wheel 2 as shown, serves to avoid fouling of the grinding wheel with the platform 17 of a blade being ground while still enabling the whole length of the blade to be ground.

The cross feed mechanism illustrated in Figure 1 may be replaced by means producing a rotary motion. This would be of particular advantage Where the shape of the work to be ground has a considerable curvature of cross section.

In some circumstances it is preferable to use an abrasive belt instead of a grinding wheel and in such a case the belt is run over a roller of appropriate shape so that the operative grinding surface of the belt will conform to the required contour and dimensions. Such an arrangement may be used with particular advantage where the transverse section of the work permits only a small diameter wheel to be used, as in the case of the concave surface of certain turbine blades.

While reference has been made to the use of a single grinding wheel operating on one face of the work at a time, the machine may be designed to operate with two gridning wheels or abrasive belts, not necessarily of the same size so that the work may be ground on simultaneously opposite faces.

The shape of the work to be reproduced may be controlled by known forms of hydraulic and electronic means or by pneumatic and electronic means instead of the mechanical means described.

Grinding tools and machines embodying the invention present numerous advantages over tools and machines at present in use. For example, the area of working surface of the wheel is very large thus tending to reduce the need for re-dressing. With normal line grinding the wheel wears rapidly over a small central portion of the total surface used thus necessitating the removal of a considerable volume of the wheel jwhenre-tlressing. the shape, whereas in the case of the wheel .describedlin the present specification, wear is even over the whole periph-' ery thus tending to reduce still further the need for redressing. Again, due to the wheel shape it is possible to grind faster than with a narrow wheelwithout sacrificing surface finish. In other words, for a given feed, grinding marks will be less pronounced than with conventional grinding due to the larger curvature of the wheels cross section. Further, the shape of the'wheel lends itself to the use of an abrasive belt as the work roller tends to centre the belt. 'Due again to the shape of the stylus and the rolling movement, wear on the stylus is reduced. The larger heat capacity of the wheel, coupled with the fact that the line on which the wheel grinds moves rapidly from one end of thewheel to the other, means that both it and the work will remain comparatively cool. Burning of the work which is often very thin, the clogging of the wheel and the breaking down of the grit bonding material can therefore more readily be avoided.

I claim:

1. A method of grinding a three-dimensional curved surface on a workpiece which comprises supporting the workpiece in engagement with a continuously rotating convex grinding surface having a width not less than the length of the curved surface and efiecting rotation of the workpiece about an axis at right angles to the axis of rotation of the grinding surface simultaneously with movement of the workpiece along a path parallel to said axis of rotation thereof, and also in a direction towards and away from the axis of rotation of the said grinding surface, thereby to generate on the workpiece the required three-dimensional surface.

' "2. A grinding machine for generating on a workpiece a three-dimensional curved surface, comprising a grinding wheel having a convex peripheral surface and supported for rotation about a fixed axis, means for effecting rotation of the grinding wheel, a workpiece supporting cradle for supporting a workpiece relative to said grinding wheel, a master cam mounted on said cradle, a surface of said master cam corresponding in shape to the said three-dimensional curved surface, a fixed stylus for engaging the said surface of the master cam, a member supporting said cradle for rotation about an axis at right angles to the axis of rotation of the grinding wheel, drive means for oscillating the cradle about said axis of rotation thereof, means slidably supporting said member for movement along a first rectilinear path radially towards and away from the grinding wheel, means biasing said member for movement along said first rectilinear path in a direction towards the grinding wheel to engage the master cam with the stylus and the workpiece with the grinding wheel, means mounting said member for movement along a secondrectilinear path parallel to the said axis of rotation of the cradle, and a cross'feed mechanism operable simultaneously with said drive means for moving said member along said second rectilinear path, whereby a workpiece supported by said cradle is simultaneously rocked about said axis of rotation of the cradle while moving towards and away from the grinding wheel under the control of the said master cam and while being moved in a direction parallel to said second rectilinear path under the control of the cross feed mechanism.

References Cited in the file of this patent UNITED STATES PATENTS 1,735,891 

